The present invention relates to screw-in fasteners which are inserted into threaded sleeves of the anchors embedded in precast concrete elements.
The tubular anchors provided with threaded sleeves, which are embedded in precast concrete elements, serve for fixing precast concrete elements to structural parts of lifting or hoisting equipment during the transportation and handling of those parts. A screw-in fastener for connecting concrete elements with a hoisting unit has been disclosed, for example in German patent publication DE-OS No. 19 13 912. The disclosed fastener includes a rope sling provided with a threaded pin. Hooks of the rope or the chain of the hoisting apparatus can hang on the rope sling.
Precast concrete elements must be usually fixed to the hoisting unit at relatively long intervals at the manufacturing plant. In many instances the fastener provided with the rope sling is screwed-in and released from the concrete element again and again, which leads to considerable labor consumption. Moreover, there is a danger that the inner thread of the sleeve of the anchor embedded in the concrete element would be contaminated.
In order to avoid the above disadvantages it has been proposed to place the fastener provided with a rope sling in the tubular anchor at least within the manufacturing plant and an eventual interpositioning. However, a comparatively great number of such fasteners have been required. But such fasteners are not suitable for a diagonal pull because of the force-in connection of the rope slings to the threaded pins, so that the carrying capacity of the fasteners during the diagonal pull decreases depending on the angle of application of the pulling force.
Anchor heads with improved diagonal pull-capacities have been also known. Such an anchor head has been described in German patent publication DE-OS No. 30 09 789. With such a construction the decrease of loads during the diagonal pull has been also required because the application of the pulling force in this case takes place only via the threaded pin.
The German patent DE-PS No. 1,684,278 teaches a transport anchor which can be connected to an anchor embedded in a concrete element in a substantially quicker and simpler manner than in the case of screw-in fasteners. These transport anchors have claws which are engaged with the head of the anchor embedded in the concrete element. The construction of the anchor embedded in a concrete element is described, for example, in DE-GM No. 82 07 185. The multiple securing and releasing of this transport anchor causes no substantial labor consumption; furthermore such transport anchors permit a diagonal pull without, however significantly decreasing a carrying capacity because the transport anchor is laterally supported on the wall of the recess provided in the precast concrete element. The advantage of the tubular anchor, as compared to the arrangement including a ball-shaped head embedded in concrete and a transport anchor with a large recess in concrete, is that the tubular anchor can be also inserted in thin plates and very slender steel concrete elements.